KR100687585B1 - Calcium carbonate synthesis method and resulting products - Google Patents

Abstract

The invention relates to a process for obtaining fibers integral with calcium carbonate particles, in which the fibers to be treated are contacted with carbon dioxide generator means and at least one composition comprising Ca++ ions capable of reacting with the carbon dioxide so as to give "in fine" a precipitation of calcium carbonate "in situ" on the fibers. Preferably, the carbon dioxide generator used is calcium bicarbonate.

Description

Calcium carbonate synthesis method and product thereby {CALCIUM CARBONATE SYNTHESIS METHOD AND RESULTING PRODUCTS}

The present invention relates to a process for synthesizing calcium carbonate in contact with fibers and to novel products obtained thereby. More specifically, the present invention relates to a method of obtaining fibers integral with calcium carbonate particles, wherein the method comprises at least one composition containing Ca ²⁺ ions capable of reacting the fibers to be treated with carbon dioxide generator means and carbon dioxide. Calcium carbonate precipitates "in fine" on the fibers "in situ".

The present invention further relates to a process for removing calcium carbonate from other insoluble compounds, in particular present in various aqueous media derived from recycled paper and ink removal sludge.

In various fields related to fibrous products, including in the field of paper pulp, it is known to provide fillers, generally inorganic fillers, to the product in order to impart specific physical properties to the product. In addition, in view of the high cost of producing and converting the fibers, fillers serve as cheaper substitutes, thereby reducing the manufacturing cost of products containing these fillers.

In particular, in the field of papermaking, in addition to the economics that fillers achieve, fillers impart a number of properties to the paper, such as opacity and whiteness, density and porosity, printability and handling.

Opacity is an essential property for paper, especially printing and writing paper, in which case it is desirable for the ink to penetrate as little as possible on the back of the sheet. For printing and other uses, whiteness is also required, which is not always represented by fibers. In this case, the papermaker adds filler.

Fillers are generally inorganic powders and are added to the fibers prior to forming the paper sheet, in which case the filler is preferably added to the pulp during the preparation of the fiber suspension fed to the papermaking machine (fillers after the sheet has dried). Is added, the pigment is preferably added by coating onto a dried paper sheet output from the paper machine, this operation is referred to as "coating").

Generally, the filler is mixed with the fibers during the preparation of the fiber suspension. Fillers, whether synthetic or natural, are prepared "ex situ", ie, sifted before being precipitated or ground and used in paper mills.

The main natural fillers are kaolin (aluminum silicate), talc (magnesium silicate) and calcium carbonate, and the main synthetic fillers are titanium dioxide, aluminum hydroxide, a mixture of aluminum sulfate and lime called "satin white", and precipitated calcium carbonate.

Recent developments in the sizing of paper in alkaline media have increased the use of calcium carbonate, both in natural and precipitated form, especially among such various fillers, and the additives are characterized by their morphological properties as well as their greater whiteness. It is playing an increasingly important role.

Fillers are added in amounts that vary depending on the paper type, i.e. 5 to 35 weight percent on average. Increasing the filler content is an economic advantage if the paper is marketed on a weight basis or on a sheet basis. That is because expensive fibers are partially replaced by inexpensive fillers. However, if the content of the filler is too high, the mechanical performance of the paper is impaired, which causes the manufacturer to use a binder and a retention aid. That is, other chemical additives are also used, including a sizing agnet that reduces the sheet's sensitivity to water and a drainage agent that facilitates flow during the formation of the sheet.

Optimizing the proportion of filler is fundamentally dependent on the shape and distribution of the inorganic crystals in the fiber. Purity and crystallographic properties of the filler affect the properties of the paper.

Therefore, paper is referred to as mixing raw materials having very different chemical and physical properties in the manufacture, formation of wet sheets by removal of water, drying of wet sheets, possible treatment of the sheet surface, and "white water". It is a composite material that requires a series of successive steps using multiple techniques for the recycling of various liquids formed from a process called.

The main raw materials are vegetable fibers and fillers, but chemical additives, most of which are expensive products, are essential for the good progress of each step. Therefore, one goal of the papermaker is to reduce the amount of the additive.

Incorporating filler into the fibers is an essential step in the papermaking process. In the many difficulties encountered in carrying out these steps, various processes and products have been proposed to improve the impact of fillers on both the papermaking process and the properties of the finished product. One of the recommended routes is to make fillers "in situ", ie in the presence of fibers, to make the fillers more efficiently retained and dispensed in a fiber mat.

Thus, US-A-2583548 discloses a method comprising impregnating cellulose fibers with a solution containing calcium chloride, followed by reacting the salts with sodium carbonate following the metathesis reaction of the two salts.

CaCl ₂ + Na ₂ CO ₃ → CaCO ₃ + 2 NaCl

Subsequently, impregnating calcium chloride into the fiber may cause calcium carbonate to precipitate into or around the fiber. Sodium chloride is a byproduct of the reaction and must be removed by washing, which complicates industrial performance.

In addition, US-A-5096539 discloses a process describing the precipitation of calcium carbonate “in situ” from calcium chloride according to the same principles as above, which removes calcium chloride located on the outside of the fiber. And washing the fiber before adding sodium carbonate to more specifically add calcium carbonate into the hollow portion of the fiber, ie the lumen. This method improves the retention and retention of mechanical properties by promoting contact between the fibers and thereby the fiber / fiber bonds (since the filler is present inside the fibers), but uses a continuous washing operation, thus providing an industrial area of the invention. This is significantly limited.

In addition, Japanese application J60-297382 discloses a method of carbonating calcium hydroxide according to the following reaction scheme.

Ca (OH) ₂ + CO ₂ → CaCO ₃ + H ₂ O

In this method, calcium hydroxide is placed in the presence of fibers. Calcium hydroxide is added in solid form. The fibers are in suspension form. The fiber should have fibrils on its surface to allow for the continuous retention of calcium carbonate. The entire batch is mixed with stirring for about 10 minutes. Subsequently, carbon dioxide is injected with stirring to carbonize the lime. This stirring step is indispensable. That is, the stirring step ensures uniformity of reaction and production of uniform particles of calcium carbonate. The reaction time depends on the proportion of lime added and the concentration of carbon dioxide. The reaction time is generally 30 minutes. This method has the advantage of not requiring a washing step, but the complex problem of having to carry out continuously remains. In particular, during the first step it is necessary to contact the milk of the lime with fibers, in particular fibrils, in a relatively concentrated medium, in which more weight of quicklime than the weight of the fibers is added. In the second step, a very important and necessary stirring step is carried out so that carbon dioxide injected into the suspension of fibers and slaked lime can react with calcium hydroxide to form crystals that trap fibrils, which is very difficult to carry out. The higher the concentration of crystals, the better the integrity of the fiber with the crystals.

In addition, US-A-5223090 applies the same scheme as described above.

Ca (OH) ₂ + CO ₂ → CaCO ₃ + H ₂ O

In a method for synthesizing CaCO ₃ "in situ" in contact with cellulose fibers, hollow fibers containing water in the interior or walls of calcium in the form of powder, ie CaO or Ca (OH) ₂ . Add to According to this method, the fibers cannot in any case be present in the form of an aqueous fiber suspension when carbon dioxide is added, which needs to be added in an amount sufficient to ensure a complete reaction. This step must necessarily be carried out in the reactor under conditions of pressure and agitation that vary with the water content of the fibers. The product obtained later in the reaction must then be transported or used as an additive to integrate the papermaking process. According to this method, in order to facilitate the mixing of lime and fibers, it is recommended to charge the fibers in a suspension with a high moisture content before adding carbon dioxide to the pressurized reactor and then centrifuging the suspension to remove moisture from the suspension. It may be desirable.

Furthermore, in the process of obtaining calcium carbonate-filled fibers "in situ" as known from French patent application 2689530, two successive steps, i.e. Application of the reaction scheme is observed, including contacting calcium hydroxide followed by addition of carbon dioxide. The method described in this French patent application has the same disadvantages as the method described in Japanese application J60-297382, namely the need for the use of a large proportion of fillers to integrate the calcium carbonate precipitate formed in order to capture fibrils, There is a need to provide a suspension containing fibril-rich fibers and, moreover, to provide a powerful mixing device for the injected gas to react with calcium hydroxide.

In addition, all the above mentioned methods have the disadvantage that the filler cannot be purified for the purpose of improving whiteness. In fact, in these methods it is impossible to remove any colored impurities present in the batch, so that such impurities are deposited on the carbonate as well as the fibers at the same time, limiting the whiteness of the paper obtained at this time.

The above-mentioned methods cannot be integrated into the current manufacturing cycle, either because they require complex washing steps, or because they present difficult chemical reactions of gaseous / liquid / solid phase type in the presence of fibers, which can be applied directly to the papermaking process. Can't.

Thus, to date, precipitated calcium carbonate with high whiteness and very well defined granulometry from any source of calcium carbonate can be produced "in situ" or consistent with that of the suspension supplied to the paper machine. There is no method of producing calcium “in situ” calcium carbonate that can be simply incorporated into a papermaking process as a method that can be applied to a fiber suspension as a diluent.

More generally, to date calcium carbonate can be removed from the aqueous medium and / or the calcium carbonate can be separated from other insoluble products in the aqueous medium, in particular in ink removal sludge derived from waste paper or recycled paper. There is no way at all.

The present invention can in particular solve the problems outlined above.

The method of the present invention comprises the steps of preparing a first composition comprising calcium bicarbonate, preparing a second composition comprising calcium hydroxide, and precipitating calcium carbonate in contact with at least some fibers. 2 composition and a fiber to be treated.

Preferably, the calcium bicarbonate present in the first composition is obtained by treating calcium carbonate with carbon dioxide.

In a first variant of the invention, at least some of the Ca ²⁺ ions are from a calcium carbonate loaded liquid.

In another variant of the invention, at least some of the Ca ²⁺ ions are from a lime solution.

In order to remove impurities, the first composition and / or the second composition is preferably filtered before mixing.

The calcium carbonate used to prepare the first composition of the present invention can be natural calcium carbonate fine particles independent of purity that can be obtained from any source present in the recovered water, or can be calcium carbonate from any other source. , Preferably in the form of an aqueous suspension containing from 0.5 g / l to 10 g / l, preferably from 1.5 g / l to 3 g / l, in particular 2 g / l.

The carbon dioxide is preferably injected in the form of pure gas or diluted in such a way that the total pressure is almost above atmospheric pressure.

Preferably, the second composition of the invention is an aqueous lime suspension, with calcium hydroxide concentration (before filtration) of 1 g / l to 10 g / l, preferably 1.5 g / l to 2.5 g / l, more preferably 2 present in g / l. The most preferred concentration corresponds to a concentration slightly above the solubility limit of calcium hydroxide in the aqueous medium under conditions of temperature and pressure used to saturate the lime solution resulting from preferential subsequent filtration.

In one variation of the invention, when using a paper machine for making paper from fibers, the paper machine discharges a residual liquid called "white water" and the first composition comprises at least a fraction of "white water" obtained from the paper machine.

In another variant of the invention, when a paper machine is used to make paper from fibers, the paper machine discharges a residual liquid called "white water" and the second composition comprises at least a fraction of "white water" obtained from the paper machine. .

In the case of making paper from fibers using paper machine, the paper machine discharges the residual liquid called "white water", and the method of the present invention allows the "white water" to be filtered into two fractions, namely "loaded-water". Separating into an unfiltered fraction called "and a filtered fraction called" clear water ", preparing a first composition using" load water ", and using" clear water " 2 preparing a composition. "Load water" comprises very fine calcium carbonate particles, and controlling the required amount of calcium carbonate is performed by adding calcium carbonate of any quality. The quality of the calcium hydroxide added to the "clear water" to prepare the second composition is likewise optional.

In the process of the invention, the first composition is a solution of calcium bicarbonate, the second composition is a solution of lime water, in particular to remove colored insoluble residues before precipitation of calcium carbonate, and (according to ISO brightness) It is very advantageous to filter the compositions before mixing to obtain calcium carbonate with a whiteness of 95 or more.

The process according to the invention can be applied to all types of fibers used in papermaking, regardless of the nature of the fibers and the degree of beating.

The fibers to be treated are preferably present in the form of a fiber suspension in water containing 1% to 15% by weight of fibers, more preferably 5% to 10% by weight of fibers.

The novel composite product according to the invention contains fibers and fillers crystallized in contact with the fibers, wherein the calcium carbonate crystals are fixed on the surface of the fibers, unitary and uniform over the entire surface of the fibers. It is characterized in that it is distributed, not aggregated or agglomerated together, regular, and having a size of 0.5 to 5 μm.

In one variant of the invention, the novel composite product is characterized in that its calcium carbonate content is from 2% to 50% by weight, preferably from 2% to 30% by weight relative to the total solids content.

According to another embodiment, the method of the present invention relates to a method for removing calcium carbonate from other insoluble materials present in various aqueous media, particularly from recycled paper and ink removal sludge, which is injected into a medium treating CO ₂ . Dissolving sodium carbonate to form bicarbonate, and separating the calcium bicarbonate formed from the medium by filtration after the reaction.

The calcium bicarbonate formed is preferably treated to produce calcium carbonate.

The solution containing calcium bicarbonate is preferably contacted with a solution of calcium hydroxide to produce calcium carbonate.

It is advantageous to filter the solution of calcium hydroxide in advance to remove insoluble impurities.

In one variant of the invention, the step of forming calcium carbonate is carried out in the presence of the fibers to produce a lysate of calcium carbonate on the fibers "in situ".

In another variant of the invention, the inert solid particles are added to one of the solutions after filtration and before mixing as the calcium carbonate seed growth initiator.

In another variant of the invention, it is preferred that the calcium carbonate is charged "out-of-the-field" in the absence of a support.

The present invention will be described more easily by the examples of the following embodiments together with the drawings, but is not limited thereto.

1 is a view of a method for synthesizing calcium carbonate in contact with the fiber in the papermaking process.

2-4 are scanning electron micrographs (SEM) of the novel product of the present invention.

5-7 are scanning electron micrographs of the control product.

The method of synthesizing calcium carbonate in contact with the fiber in the papermaking process is shown in FIG. 1 according to the method of the present invention.

"White water" is separated into two fractions by filtration in separator 1, i.e., a filtered fraction without calcium carbonate forming "transparent water" and an unfiltered fraction enriched with calcium carbonate forming "load water". do.

"Transparent water" is used to prepare the milk of lime. For this purpose, the "clear water" is transferred into the calcium hydroxide mixer 2 to which lime is added. The quality of lime added is optional and includes, for example, quicklime, slaked lime, lime residue, or residues from waste paper incinerators. The amount of lime is determined such that the milk of lime preferably has a concentration slightly above the solubility limit of calcium hydroxide under the operating conditions. The milk of the lime is filtered in a lime water filter 3 to remove impurities from the lime added and residual impurities from the regenerated water.

The calcium carbonate load water is injected into the carbonation unit 4 at a constant concentration by adding calcium carbonate of any quality. This load is treated with gaseous CO ₂ to convert insoluble calcium carbonate to calcium bicarbonate, which is more soluble according to the following known scheme.

CaCO ₃ + CO ₂ (gas) + H ₂ O → Ca (HCO ₃ ) ₂

In this way a saturated solution of soluble calcium bicarbonate is prepared, which contains from 1 g / l to 3 g / l of Ca (HCO ₃ ) ₂ or more. The resulting solution is filtered in a bicarbonate filter 5 to remove insoluble impurities from regenerated water and from calcium carbonate to be added, in particular to remove colored insoluble residues.

According to another embodiment of the present invention, pure or nearly pure calcium carbonate converts insoluble calcium carbonate present in any recoverable solution into soluble calcium bicarbonate, and then contains an aqueous solution containing particles on one side and bicarbonate on the other side. Prepared by separation into the precipitate, which is eventually precipitated on the fibers or "out-of-the-field". Therefore, this method of obtaining calcium carbonate can recover the calcium carbonate present in the various aqueous media associated with (or not) the papermaking process, especially aqueous media derived from recycled paper and ink removal sludge. In this specific embodiment of the present invention, the aqueous medium containing calcium carbonate among other insoluble compounds is filtered after treatment with CO ₂ . The aqueous phase containing calcium bicarbonate can be treated to produce calcium carbonate, which is usually added to the separator 1 or otherwise used in the context of the present invention, which also contains calcium bicarbonate. The aqueous phase can be added directly to the crystallization tank 6 by adjusting the concentration, or otherwise used in the context of the present invention.

Subsequently, the filtration performed on the solution containing calcium ions makes it possible to obtain calcium carbonate crystals with high whiteness.

The fibers to which the method of the invention is applied are derived from the paper machine upstream of the process. The fibers here are in the form of an aqueous suspension and are beaten according to the desired final properties of the paper. The present invention can be applied to any case where the degree of beating is any.

The solution containing calcium bicarbonate, calcium hydroxide and fiber suspension is then mixed in the crystallization tank 6 in a continuous manner or batchwise depending on the requirements and equipment of the manufacturing process. Mixing rates and mixing times vary to optimize the crystallographic form.

The crystallization of calcium carbonate is then carried out on the fibers according to the following scheme.

Ca (HCO ₃ ) ₂ → CaCO ₃ + CO ₂ + H ₂ O

Since the pH is less than 8, the CO ₂ dissociated during the reaction is consumed immediately, and calcium hydroxide occurs in any case according to the following equation.

Ca (OH) ₂ → 2 CO ₂ → Ca (HCO ₃ ) ₂ or Ca (OH) ₂ + Ca (HCO ₃ ) ₂ → 2CaCO ₃ + 2H ₂ 0

 The advantage of the product obtained according to the invention is measured not only by the quality of the whiteness formed from the purification by filtration, but also by the ratio of the crystals fixed in contact with the fibers and by the morphological properties of the crystals formed thereby. (Described below).

Example 1

The following examples are intended to more easily illustrate the invention.

Three solutions were prepared as follows.

Aqueous solution A = 9.60 g or 120 g solution containing 80 g / l vegetable fiber.

Aqueous solution B = 1.60 g or 970 g solution containing 1.60 g / l Ca (OH) ₂ .

1600 g solution containing aqueous solution C = 3.5 g or 2.2 g / l Ca (HCO ₃ ) ₂ .

Solution B was prepared in a beaker containing 2000 g of water. 6 g of quicklime, CaO were added. The mixture was stirred at rt for 10 min. The solution was filtered to remove residual product in suspension and then diluted to adjust the concentration to 1.6 g / l Ca (OH) ₂ . 970 g of the solution was obtained.

Solution C was prepared at room temperature in a reactor containing 2000 g of water and equipped with an automatic suction turbine. 6 g of CaCO ₃ ground to 10 μm was added and the reactor was sealed, then CO ₂ gas was injected under a pressure of 3 bar and this pressure was maintained for 5 minutes. Subsequently, decompression and slight vacuum were performed to remove dissolved CO ₂ , and then the solution was filtered and diluted to remove residual product in the suspension, thereby reducing the concentration to 2.2 g / l Ca (HCO ₃ ) _2. Adjusted to. 1600 g of the solution was obtained.

A + B + C was mixed with stirring in the vessel. No other additives were added.

Sufficient amount of suspension was taken to prepare paper specimens according to procedures known to those skilled in the art.

After drying, the paper swatches were collected and the calcium carbonate attached to the fiber was measured by comparing the amount of calcium carbonate precipitated during mixing of solution B and solution C.

The proportion of calcium carbonate fixed to the fiber was 60%. The sample contained 20.2 wt% calcium carbonate.

Taken by scanning electron microscopy at magnification 503, FIG. 2 consists of basic fibers containing crystals of calcium carbonate that are uniformly distributed throughout the product without the formation of aggregates or agglomerates according to the invention. Shows that it exists in the form of a fibrous structure.

3 taken at a magnification of 2500 shows that the crystals are single and stick to the fibers. The size of the crystals was regular, about 3 μm.

4 taken at a magnification of 10,000 illustrates the growth of crystals. In this case, the crystal was a rhombohedral structure.

Example 2: Comparative Example

This example was carried out using commercially available calcium carbonate, namely “precipitated,” product 92 E from SOLVAY. In this second embodiment, the filler was simply mixed with the fibers according to conventional routes known to those skilled in the art.

Aqueous solution A = 9.6 g or 120 g solution containing 80 g / l vegetable fiber.

2570 g solution containing aqueous solution B = 4.30 g or 1.70 g / l carbonate 92 E.

In the same manner as in Example 1, A + B was mixed and paper samples were prepared under the same conditions.

After drying, the paper sample was recovered and measured by comparing the amount of calcium carbonate precipitated from solution B with the calcium carbonate held by the fiber.

The proportion of calcium carbonate retained by the fiber was 15% without chemical additives. The sample contained only about 60% by weight calcium carbonate.

5 taken by scanning electron microscopy at magnification 503 shows that the control product is in the form of a fibrous structure consisting of basic fibers containing aggregates of calcium carbonate crystals distributed irregularly throughout the product.

6, taken at a magnification of 2500, shows that the crystals are agglomerated and irregular in size.

7, taken at a magnification of 10,000, shows that highly aggregated crystals capture fibrils. In this case, the crystal was a scalenohedral structure.

These examples illustrate the advantages of the bicarbonate route according to the invention over the conventional route. The precision of calcium carbonate on the fibers was much greater when the bicarbonate route was adopted.

The crystals are single, fixed to the walls of the fibers, and not aggregated or agglomerated.

The crystal showed a very planar shape. The crystals were uniform in size. The size of the crystal varied mainly within 0.1 μm to 10 μm, preferably 0.5 μm to 5 μm, depending on the mixing rate as well as the concentration and temperature of the solution. The crystals were smaller when the mixing rate or temperature was higher and when the amount of calcium carbonate was small.

While not wishing to be bound by any one theory, Applicants claim that the method according to the present invention, in contrast to what happens when precipitated "in situ" from calcium hydroxide alone, has the following characteristics: It is observed that calcium bicarbonate is used as a starting material for preparing carbonates, that the reaction occurs in microdomains where the pH is acidic (about 6 at the beginning of the reaction) and that it is in contact with the fibers. Crystals of calcium carbonate grow from seeds present on and within the fibers. This assumption is supported by the fact that the calcium carbonate crystals according to the invention are in the form of flat crystals, which are the properties of the crystals obtained from supersaturated solutions by crystal growth.

In contrast, in the case of precipitation of calcium carbonate from Ca (OH) ₂ , the reaction takes place in the basic medium, and the precipitation which takes place on the fiber by mechanical bonding rather than by chemical bonding is smaller than that described in French patent application 2689530. Observed by agglomeration of crystals, but not by crystal growth.

Such structural differences in the product may explain the better retention of fillers in the fiber.

The process according to the invention can be applied to all pulp of mechanical or chemical origin regardless of the degree of beating. In addition, the process of the present invention can be applied to fully or partially recycled pulp, in which the fiber or fiber mixture, recycled form or other forms must be dissolved in the manner described above for introduction into the crystallization tank 6.

Embodiments of the present invention relating to removal of calcium carbonate or separation of calcium carbonate from other insoluble materials are demonstrated from the following examples.

Calcium carbonate present in the ink removal sludge or other sludge is converted to calcium bicarbonate according to the method of the present invention described above. Since the bicarbonate is soluble, this solution only needs to be filtered to produce water containing on the one hand the bicarbonate dissolved therein and on the other hand all the insoluble substances retained in the filter. This makes it possible to recover the carbonate and / or recover the sludge containing no calcium carbonate by reprecipitating the carbonate according to the application to which the present invention is intended.

Claims (27)

Integrate with the calcium carbonate particles by contacting the fibers to be treated with carbon dioxide generator means and one or more compositions comprising Ca ²⁺ ions capable of reacting with carbon dioxide to “fine” precipitate calcium carbonate on the fibers “in situ”. In the method of obtaining the obtained fiber, Preparing a first composition comprising calcium bicarbonate, Preparing a second composition comprising calcium hydroxide, and Mixing the first composition, the second composition and the fibers to be treated so that calcium carbonate precipitates in contact with the fibers Method comprising a. The method of claim 1 wherein the calcium bicarbonate present in the first composition is obtained by treating calcium carbonate with carbon dioxide. The method of claim 1 or 2, wherein some or all of the Ca ²⁺ ions are from a calcium carbonate loaded liquid. The method of claim 1 or 2, wherein some or all of the Ca ²⁺ ions are derived from a lime solution. The method of claim 1 or 2, wherein the first composition is filtered before mixing. The method of claim 1 or 2, wherein the second composition is filtered before mixing. The process of claim 2 wherein the calcium carbonate is in the form of an aqueous suspension containing 0.5 g / l to 10 g / l. 3. The method of claim 2, wherein the carbon dioxide is injected in the form of pure gas or in a diluted form such that the total pressure is above atmospheric pressure. The method of claim 1 or 2, wherein the second composition is an aqueous lime suspension and the concentration of calcium hydroxide (prior to filtration) is between 1 g / l and 10 g / l. The method according to claim 1 or 2, characterized in that the calcium bicarbonate present in the first composition is derived from calcium carbonate present in the aqueous medium by treating the aqueous medium discharged from the recycled paper and the ink removal sludge with carbon dioxide. How to. The method of claim 1 or 2, characterized in that the first composition comprises some or all of the fraction of "white water" obtained from a paper machine which is used to make paper from fibers and discharges residual liquid called "white water". How to do. The method according to claim 1 or 2, characterized in that the second composition comprises some or all of the fraction of "white water" obtained from a paper machine which is used to make paper from fibers and discharges residual liquid called "white water". How to do. The method according to claim 1 or 2, The "white water" obtained from the papermaking machine used to make paper from the fibers and discharge the residual liquid called "white water" into two fractions by filtration, the unfiltered fraction called "load water" and the "clear water". Separating into filtered fractions called, Preparing a first composition using “load water”, and Preparing a second composition using “transparent water” Method comprising a. The method according to claim 1 or 2, wherein the first composition is a solution of calcium bicarbonate, the second composition is a solution of lime water, and these compositions remove colored insoluble residues, especially before precipitation of calcium carbonate, Filtration before mixing to obtain calcium carbonate having a whiteness of 95 or more). 3. The process according to claim 1, wherein the fibers to be treated are in the form of an aqueous fiber suspension containing 1% to 15% by weight of fibers. A composite product containing fibers and fillers that crystallize in contact, The crystallized filler in contact with the fiber is a crystal of calcium carbonate, The crystals are single, uniformly distributed throughout the fiber surface, do not agglomerate or agglomerate together, The crystals are regular, the composite product, characterized in that the size of 0.1 ㎛ to 10 ㎛. The composite product according to claim 16, wherein the content of calcium carbonate is 2% to 50% by weight relative to the total solids content. 18. The composite product of claim 16 or 17, wherein the composite product is in the form of a wet sheet. The method of using the composite product of Claim 16 or 17 at the time of manufacture of a filled paper. In particular a method for separating or removing calcium carbonate from other insoluble materials present in various aqueous media derived from recycled paper and ink removal sludge, Injecting CO ₂ into the medium to be treated, Dissolving calcium carbonate to form bicarbonate, and Separating the calcium bicarbonate formed from the medium by filtration after the reaction Method comprising a. delete 21. The method of claim 20, wherein the solution containing calcium bicarbonate is contacted with a calcium hydroxide solution to produce calcium carbonate. 23. The method of claim 22, wherein the calcium hydroxide solution is prefiltered to remove insoluble impurities. 24. The method of claim 22 or 23, wherein the step of forming calcium carbonate is carried out in the presence of the fiber to precipitate calcium carbonate on the fiber "in situ". 24. The process according to claim 22 or 23, wherein inert solid particles are added as calcium carbonate seed growth initiator to one of the solutions after filtration and before mixing. 24. The method of claim 22 or 23, wherein the calcium carbonate precipitates "out site" in the absence of a support. 20. The method of claim 19, wherein the filled paper is writing paper, printing paper, newspaper, tobacco paper or fine paper.

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